Uranium contamination of bivalve Mytilus galloprovincialis, speciation and localization
Résumé
Uranium is a natural radioelement (also a model for heavier actinides), but may be released through anthropogenic
activities. In order to assess its environmental impact in a given ecosystem, such as the marine system, it
is essential to understand its distribution and speciation, and also to quantify its bioaccumulation. Our objective
was to improve our understanding of the transfer and accumulation of uranium in marine biota with mussels
taken here as sentinel species because of their sedentary nature and ability to filter seawater.
We report here on the investigation of uranium accumulation, speciation, and localization in Mytilus galloprovincialis
using a combination of several analytical (Inductively Coupled Plasma Mass Spectrometry, ICP-MS),
spectroscopic (X ray Absorption Spectroscopy, XAS, Time Resolved Laser Induced Fluorescence Spectroscopy,
TRLIFS), and imaging (Transmission Electron Microscopy, TEM, μ-XAS, Secondary Ion Mass Spectrometry, SIMS)
techniques. Two cohorts of mussels from the Toulon Naval Base and the Villefranche-sur-Mer location were
studied. The measurement of uranium Concentration Factor (CF) values show a clear trend in the organs of
M. galloprovincialis: hepatopancreas ≫ gill > body ≥ mantle > foot. Although CF values for the entire mussel are
comparable for TNB and VFM, hepatopancreas values show a significant increase in those from Toulon versus
Villefranche-sur-Mer.
Two organs of interest were selected for further spectroscopic investigations: the byssus and the hepatopancreas.
In both cases, U(VI) (uranyl) is accumulated in a diffuse pattern, most probably linked to protein complexing
functions, with the absence of a condensed phase.
While such speciation studies on marine organisms can be challenging, they are an essential step for deciphering
the impact of metallic radionuclides on the marine biota in the case of accidental release. Following our
assumptions on uranyl speciation in both byssus and hepatopancreas, further steps will include the inventory and
identification of the proteins or metabolites involved.